Britain on Wednesday asked Sri Lanka to probe allegations that hundreds of men and women had been sexually assaulted by government forces during and after the island's drawn-out ethnic war.
Foreign Secretary William Hague told a public meeting in the Sri Lankan capital Colombo that Britain was concerned that no-one had been held accountable for rights abuses, including sexual assault and the use of rape to extract confessions.
He said there had been credible allegations, including those from a UN Panel of Experts, that Sri Lankan troops used sexual violence during their war against Tamil rebels and afterwards.
"I will be urging the Sri Lankan government to investigate these cases as they deserve," Hague said.
Prime Minister David Cameron also promised to "shine a spotlight" on Sri Lanka's rights record ahead of a meeting of the Commonwealth Heads of Government in Colombo on Friday.
"Being in Sri Lanka does mean it's an opportunity to shine a spotlight on some of the problems there, some of the human rights issues," he said. "It's right to do that and that's exactly what I'll be doing."
Cameron was responding to criticism from Sri Lanka's minister of mass media and communication, who dismissed the British premier's calls for an inquiry into alleged war crimes.
"We are a sovereign nation," Keheliya Rambukwella told the BBC. "You think someone can just make a demand from Sri Lanka.
"It can be a cordial request. We are not a colony. We are an independent state."
The New York-based Human Rights Watch (HRW) reported earlier this year that Sri Lankan security forces continue to use rape and other forms of sexual violence to torture suspected Tamil rebels four years after the end of the island's civil war.
HRW also claimed widespread rape of detainees during the separatist conflict that ended in May 2009.
Hague said there had been "progress" in economic development, clearing land mines and re-integrating some of the former rebels back in society.
But he said no-one had been held accountable for sexual crimes during and after the war ended.
"To date, nobody has been held to account for crimes of sexual violence," he said ahead of the Commonwealth meeting.
Canadian Prime Minister Stephen Harper is leading a boycott of the summit. The prime ministers of India and Mauritius are also staying away from the meeting over Sri Lanka's human rights record.
Cameron has also been under pressure to boycott the event, but he has promised to have "tough conversations" with President Mahinda Rajapakse about issues of accountability.
International rights groups say up to 40,000 civilians were killed by government forces in the final months of fighting in 2009, but the government has denied it killed a single civilian and has resisted calls for an international probe.